In many transducers, a member is caused to be moved in correspondence with a measured parameter (measurand). The relative position of the movable member is sensed, as by the use of a linear motion potentiometer to thereby generate an electrical signal corresponding to the relative position of the movable member, which thus in turn corresponds to the measured parameter. This dependence on the sensing of the relative position of the movable member may create error in the zero position due to the difference in the coefficient of thermal expansion of the various materials employed including the support housing, the movable member and in a transducer driver element, such as an aneroid, which causes the movable member to undergo its displacement.
In addition, the manufacturing tolerances may not insure the initial positioning of the movable member in the zero or null position.This is a problem particularly in potentiometer designs in which a wiper contact is positioned in a neutral position with respect to the resistive element.
In the case of a pressure transducer having an aneroid, bellows, or diaphragm element which is drivingly connected to the movable member causing its relative position to change in correspondence with pressure change, there are further problems in producing an accurate output signal. Some of these problems relate to the thermal characteristics of the aneroid in that the incremental movements produced by incremental changes in pressure may vary with temperature changes undergone by the unit.
It is desirable for most applications that the electrical output signal should bear a linear relationship with respect to the pressure changes in the interest of greater accuracy and simpler processing of the pressure signal in the control systems within which such pressure signal is utilized.
In automotive fuel control systems, such pressure sensor signals are currently being proposed to sense engine intake manifold pressure so as to achieve efficient fuel management. In this context, many of these problems are encountered due to the widely varying ambient temperature conditions and the relatively impreciseness of the tolerances to which such devices are manufactured. Furthermore, in such environments, such devices have to be highly reliable and very desirable to operate with little or no maintenance for long periods of time.
Accordingly, it is an object of the present invention to provide a combination of compensation features for a transducer of the type in which a movable output member is positioned in correspondence with a sensed parameter.
It is a further object of the present invention to provide such compensation features which substantially correct errors due to temperature variations experienced by the unit.
It is a further object of the present invention to provide for compensation of the zero position of the movable member to compensate for the effects of manufacturing tolerances built up in the components.
It is yet another object of the present invention to provide a compensation feature specifically for a pressure transducer in which the movement of the input member in correspondence with the sensed parameter has a tendency to vary with temperature conditions.
It is another object of the present invention to provide a transducer compensation which linearizes the electrical output signal generated in correspondence to the nonlinear displacement of a movable member.
It is another object of the present invention to provide a pressure transducer incorporating an aneroid, bellows, or diaphragm element variably positioning a movable output member which incorporates the compensation features described.